The biogas produced by the anaerobic digestion plant, depending on the opportunities, can be enhanced in the form of electricity and/or thermal energy, or it can be purified and refined for the production of biomethane.
The desulphurized and dehumidified biogas is sent to a cogenerator for the combined production of electricity and thermal energy.
- According to national legislation, all or part of the electricity is given to the electricity grid.
- The thermal energy recovered from combustion, net of the energy necessary for the maintenance of the biological process, can feed a district heating network or other utilities.
The main desulphurization methods are:
- Precipitation of sulphide directly into the digester through the addition of chemical compounds
- Internal or external biological desulphurization with air or oxygen
- Chemical washing
- Adsorption on metal oxides or activated carbon
The desulphurized and dehumidified biogas is subjected to a purification process, in order to separate the methane from the other gases that make up the biogas mixture.
The biomethane thus obtained can be used, marketed and transported in gaseous or liquefied form, like natural gas, and constitutes a programmable and cumulable resource, thanks to the wide storage capacity and the capillarity of the natural gas network present in Italy.
The possible final destinations of biomethane are:
- natural gas transmission or distribution network
- CNG refueling stations located more or less near the plant
- LNG filling stations to power heavy vehicles
IES Biogas builds turnkey plants, using the most appropriate technology for specific environmental, technical and economic needs.
The methane is separated exploiting the gas permeability characteristics of the particular materials that make up the membranes.
The process consists in conveying the biogas under pressure through a material that is not very permeable to methane and easily permeable to other gases. The result is the separation of biogas into two streams:
- an external one consisting mainly of methane
- an internal one consisting mainly of carbon dioxide
Multiple stages of separation increase process efficiency.
1 – COMPACT AND MODULAR SYSTEMS
2 – NO HEAT REQUEST
3 – HIGH PRESSURE OUTLET
The methane is separated by exploiting the different solubility characteristics of the various biogas components in an aqueous solution. Carbon dioxide, which has a solubility in water higher than that of methane, goes into solution with pressurized water. In the next phase, the aqueous solution is regenerated with a reduction in pressure which releases carbon dioxide.
1 – NO USE OF ADDITIVES
2 – NO HEAT REQUIRED
3 – OPERATIONAL SIMPLICITY
PSA (pressure swing adsorption)
Biogas components other than methane are captured in a porous material which is then regenerated by alternating cycles of pressure increase and decrease. The operating principle is the adsorption and the use of multiple adsorption lines, which allows the continuity of the process.
1 – NO USE OF LIQUIDS
2 – DRY BIOMETHANE
3 – NO HEAT REQUEST
The methane is separated by exploiting the different solubility characteristics of the various biogas components in an organic or inorganic solution. The operating principle (absorption) is the same as washing with water with the only difference that the liquid used is an organic solution that is regenerated with heat.
1 – SOLVENT REGENERATION
2 – GOOD EFFICIENCY
3 – COMPACT PLANTS